A common strain of methicillin-resistant Staphylococcus aureus may be a wolf in sheep's clothing.

The deadly USA300 strain, which swept across the country in the 1990s and currently lurks in NFL locker rooms, appears to have swiped genetic components from benign skin bacteria. Some of the borrowed genes make the microbe immune to toxins secreted by human skin, researchers report December 17 in mBio.

USA300's acquired immunity may have allowed the strain to spread unnoticed and elbow out other — less dangerous — forms of staph on the skin, the authors suggest.